1. Field of the invention
The present invention relates to a refrigerating apparatus, and more specifically to the improvement of a refrigerant heating type air conditioner.
2. Description of the prior art
A refrigerant heating type of air conditioner is generally known. For example, in U.S. Pat. No. 4,905,894 discloses an air conditioner provided with heater means for heating refrigerant in an external heat-exchanger.
FIG. 1 is a schematic iiiustration of a conventional refrigerant heating type air conditioner. A detailed description of the conventional apparatus forms part of the description of the corresponding features of the preferred embodiments of the present invention, which are identified by the same reference characters in FIGS. 1, 2 and 3. The conventional air conditioner includes heating means employed when an air conditioner operates in a heating mode. A compressor discharges refrigerant to a closed circuit known as a refrigerant circuit. In the heating mode, the refrigerant, which has been condensed in an inner heat-exchanger is supplied to the external heat-exchanger serving as an evaporator through an expansion valve. The refrigerant in the evaporator absorbs heat from the heating means and is vaporized. The vaporized refrigerant then returns to the compressor. A two-way valve is disposed at a suction port side of the compressor and the evaporator that the refrigerant in the heating mode returns to the compressor if the two-way valve is opened. When the air conditioner operates in a cooling mode, the refrigerant discharged from the compressor first flows to another external heat-exchanger or a condenser in which the refrigerant is condensed. The condensed refrigerant is then supplied to the inner heat-excahnger through the expansion valve. The two-way valve prevents the refrigerant flowing through the first external heat-exchanger to the compressor in the cooling mode. A check valve is provided to shutdown the fIow of the refrigerant to another heat-exchanger or the condenser in the heating mode.
The air conditioner desoribed above has a disadvantage in that a state may exist in which both the two-way valve is closed for and the expansion valve is closed during the heating mode. In such a state the refrigerant is trapped in the evaporator. The trapped refrigerant is heated and the pressure of the trapped refrigerant will greatly increased thereby damaging various parts of the air conditioner.